[nomadking]

Assuming we're talking about benefits, eg ESA.
Using a "fit note" is firstly of use in the assessment phase. Once a DWP decision has been made, you can use "fit notes" during the appeal process to continue claiming until the appeal has been heard.
IIRC the DWP ask the GP to fill out a form detailing things you can and cannot do.
Simply providing a "fit note " is not enough. Otherwise it would be pointless them detailing each activity and descriptor and awarding points against each one. Wouldn't need a claim form either.